This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-261095 filed Aug. 30, 2001.
The present invention relates to a control apparatus and method for controlling an alternating current generator mounted on vehicles, and more particularly to the control apparatus and method which outputs abnormality information to an external apparatus.
It is recently proposed to use the power generation ratio of an alternating current (a.c.) generator as a parameter in an engine control thereby to stabilize idling rotation of the engine. In JP-U-60-18120, an a.c. generator is constructed to output to an external electronic apparatus a field coil voltage signal from the junction between its field coil and its voltage regulator through a current limiting resistor. The external apparatus is thus enabled to estimate mechanical torque or the like of the generator from the power generation ratio of the generator and control an idle control valve of an engine for stabilizing the engine idle speed.
The external apparatus requires as much information as possible for engine control. Such information includes, in addition to the power generation ratio, malfunction indicative of malfunction of the generator. However, because the field coil voltage signal does not include such information other than the power generation ratio, additional signal wires must be added to the field coil voltage signal wire. It is not desirable to increase signal wires, because wiring the signal wires becomes complicated and breakage and shorting of the signal wires become more likely.
It is therefore an object of the present invention to provide an a.c. generator control apparatus and method which enables detection of malfunction of an a.c. generator without increasing signal wires.
According to the present invention, current supply to a field winding of an a.c. generator is turned on and off in a variable duty ratio within a predetermined range at every predetermined cycle period thereby to regulate an output voltage of the generator. A power generation ratio output signal is produced in a pulse form having a duty ratio corresponding to the duty ratio of the current supply to the field winding. The output signal is transmitted to an external apparatus through a signal wire. The output signal transmitted to the external apparatus is changed depending on whether an abnormality in the a.c. generator is detected. The change of the output signal may be a change of the duty ratio of the output signal to a duty ratio that is outside the predetermined range. Alternatively, the change may be a stop of transmission of the output signal to the external apparatus for a period longer than the predetermined cycle period.